1. Field of the Invention
The present invention relates to a method for manufacturing a package for electronic components including a plurality of boards which are bonded to each other so as to form a cavity at an inner side thereof and penetration electrodes that electrically connect the inside of the cavity to the outside of a base board among the plural boards.
2. Description of the Related Art
Recently, piezoelectric vibrators utilizing quartz crystal or the like have been used in cellular phones and portable information terminals as the time source, the timing source of a control signal or the like, a reference signal source, and the like. Although there are various piezoelectric vibrators of this type, an SMD (Surface Mount Device)-type piezoelectric vibrator is one known example thereof. As the piezoelectric vibrator of this type, a three-layered piezoelectric vibrator in which a piezoelectric board having a piezoelectric vibrating reed formed thereon is bonded to be interposed between the base board and a lid board is generally known. In this case, the piezoelectric vibrating reed is mounted on the base board and accommodated in a cavity that is formed between the base board and the lid board.
Moreover, in recent years, instead of the three-layered piezoelectric vibrator, a two-layered piezoelectric vibrator has also been developed. The piezoelectric vibrator of this type has a two-layered structure in which a base board and a lid board are directly bonded and packaged, and a piezoelectric vibrating reed is accommodated in a cavity formed between the two boards. The two-layered piezoelectric vibrator is suitably used in that it is excellent in achieving a thin profile compared with the three-layered structure.
As an example of a method for manufacturing such a packaged two-layered piezoelectric vibrator, a package manufacturing method in which a conductive member such as a silver paste is filled in penetration holes formed in a base board made of a glass material and baked so as to form penetration electrodes, and quartz crystal vibrating reeds in a cavity are electrically connected to the outer electrodes provided outside the base board is known. However, according to this method, there is a case where since a very small gap is present between the penetration holes and the conductive member, outer air enters into the package to deteriorate the degree of vacuum of the inside of the package, and as a result, causing deterioration in the properties of a quartz crystal vibrator. As countermeasures thereof, as proposed in JP-A-2003-209198, JP-A-2002-121037, and JP-A-2002-124845, a method of preventing deterioration of the degree of vacuum by inserting core portions made of a conductive metallic material into the penetration holes formed in a base board wafer and heating the core portions and the base board wafer to a temperature equal to or higher than the softening point of the glass so as to weld the glass and the electrode pins to each other is known.
However, in the method disclosed in JP-A-2003-209198, JP-A-2002-121037, and JP-A-2002-124845, penetration holes for inserting core portions are formed in the base board wafer using penetration hole forming pins while heating the base board wafer made of a glass material. Therefore, the glass material will swell up from both surfaces of the base board wafer near portions where the penetration holes are opened. Moreover, when the base board wafer is welded to the core portions, both ends of the core portions inserted into the penetration holes protrude from the base board wafer. Therefore, when both surfaces of the base board wafer are polished in a subsequent step to manufacture a base board having high shape accuracy with a high degree of flatness, the swelling of the glass material on both surfaces of the base board wafer and the protruding core portions become obstacles at the time of polishing, and the polishing cannot be performed well. Even if it is possible to polish both surfaces, cracks may be formed in the glass material near the core portions to cause short-circuiting of the electrode film, and a glass board wafer may be broken. In addition, the degree of flatness of the glass board wafer becomes greatly uneven.
Moreover, since the core portions have an approximately cylindrical shape, it is difficult to insert the core portions into the penetration holes of the base board wafer, the core portions are easily displaced during the welding, and thus the workability is poor.